326 PEOF. ST. GEOEaE MIVAET ON THE 



The hypapopliysis is much smaller than in the fifteenth vertebra, and springs from 

 close to the preaxial margin of the centrum. 



A slightly marked ridge runs postaxiad and externad from a point mesiad of the 

 parapophysial root of the bony bridge above described. These lateral ventral ridges 

 are the serial representatives of the catapophysial ridges of more preaxial vertebrae, 

 and each ends postaxially in a small transverse process, which projects externad on a 

 line just postaxiad to the whole. For the first time since the fourth vertebra, we here 

 find the postzygapophyses extending postaxiad decidedly, though very little, beyond 

 their articular surfaces. 



The Ceevico-doesal Veetebka. 



The SEVENTEENTH VEETEBEA again exaggerates the character of its serial predecessor. 

 The whole vertebra is antero-posteriorly shorter, and in fact somewhat smaller in 

 nearly all dimensions ; but the transverse processes and metapophyses (seen dorsally) 

 are much as in the sixteenth vertebra. The zygapophyses are a little smaller. The 

 neural spine is antero-posteriorly extended at its tip, whilst its postaxial fossa is so 

 postaxial that it is invisible when viewed dorsally. The neural spine broadens out 

 postaxially, exhibiting, dorsally, a median ridge and two lateral ones diverging from a 

 common point postaxiad. 



The hyperapophyses project as two little pointed processes, one above each postzyg- 

 apophysis. The preaxial articular surface of the centrum widens out still more, and 

 looks entirely preaxiad, or only very slightly indeed ventrad. The postaxial central 

 surface looks postaxiad. 



The hypapophysis is smaller, and the ridges on each side of its root fainter. 



There is no lateral vertebral canal. Such a canal is inclosed only by the help of the 

 rib ; and to support this there are two distinct articular facets — a parapophysial one a 

 little postaxiad of the lateral margin of the preaxial articular surface of the centrum, 

 and another diapophysial one beneath the postaxial end of the antero-posterior ridge of 

 the transverse process. 



The prsezygapophyses do not project so far preaxiad as does the centrum. 



The seventeenth vertebra is in one line with the eighteenth. 



The Doesal Vertebra. 

 The eighteenth vertebra is slightly smaller than the seventeenth. The preaxial 

 surface of the centrum is less wide transversely ; the same is the case with its postaxial 

 surface, which is also not at all concave at its ventral margin. The hypapophysis is 

 rudimentary and has no ridges on each side of its root. The transverse process is 

 somevs'hat less produced postaxially. The neural spine and its postaxial fossa are both 

 smaller. The prsezygapophyses fall still further short of attaining the preaxial end of 

 the centrum, while the postzygapophyses extend rather less postaxially beyond the 



